1. Field of the Invention
The present invention relates to a flame-retardant phenolic resin and to a process for producing the same, and, more particularly, it relates to a flame-retardant phenolic resin having excellent electrical properties, impact resistance and punchability and to a process for producing the same.
2. Description of the Prior Art
Heretofore, phenolic resins have been recognized to be excellent materials for various uses, e.g., in forms such as molded articles, laminated plates and the like from the standpoints of electrical and mechanical characteristics, cost of materials and the like. However, phenolic resins themselves are generally combustible, and in terms of safety of domestic and industrial equipment, i.e., to prevent fires, the demand for rendering phenolic resins flame-retardant has been recently increased gradually. Further, the develop domestic and industrial devices with new functions, the requirement of the characteristics of phenolic resins have become severe. Specifically, in addition to flame-retardancy, more severe requirements have been demanded for phenolic resins with respect to flexbility (plasticity) and impact resistance which are considered general disadvantages of thermosetting resins.
In order to improve the above-mentioned disadvantages, specifically flame-retardancy, of phenolic resins, various methods have been attempted. For example, to render phenolic resins flame-retardant, addition of various kinds of conventional flame-retarders to phenolic resins as disclosed in U.S. Pat. Nos. 3,352,744, 3,377,317 and 3,409,571, has been attempted but this approach is not satisfactory in achieving sufficient flame-retardancy in phenolic resins and also involves deterioration of electrical characteristics, impact resistance and punchability due to the addition of the flame-retarders. Further, in order to enable punching processing at low temperatures (e.g., room temperature) the phenolic resins must be modified with combustible oils or fats whereby a higher degree of flame-retardancy is required for phenolic resins.
Thus, practically useful phenolic resins have not heretofore been produced and development of a method for rendering phenolic resins sufficiently flame-retardant without deteriorating the other characteristics of phenolic resins is strongly desired.
The present invention was achieved in compliance with the above-mentioned requirement.